This present application relates generally to methods, systems, and/or apparatus for improving the efficiency and/or operation of turbine engines, which, as used herein and unless specifically stated otherwise, is meant to include all types of turbine or rotary engines, including gas turbine engines, aircraft engines, steam turbine engines, and others. More specifically, but not by way of limitation, the present application relates to systems and apparatus pertaining to improved seals for turbine engines.
The performance of a turbine engine is largely affected by its ability to eliminate or reduce leakage and/or the usage of cooling air. Leakage generally results from a pressure difference that exists across a leakage gap. Though it is possible to reduce the pressure difference across the leakage gap, this can place an undesirable limitation on the aerodynamic design of working fluid velocity components. The reduction of the gap itself is desirable, but its elimination is usually not practical due to inevitable different thermal characteristics between the rotating and stationary components, and the centrifugal characteristics of the rotating components. With the added considerations of component manufacturing tolerances and variation in operating conditions, which govern thermal and centrifugal characteristics, it is generally the case that a leakage gap forms during certain significant operating conditions.
In the case of gas turbine engines, cooling air is often routed directly from the compressor to turbine components to protect them from the extreme temperatures of the hot-gas path. The cooling air may be used to directly cool parts or, in some cases, may also be used to purge cavities that are open to the working fluid ingestion though the gaps that exist along the hot-gas path. Generally, to purge cavities, an out-flow of cooling air is created (i.e., a flow of cooling air from the cavity into the hot-gas path) and this out-flow substantially prevents the in-flow of working fluid through the gaps. However, like leakage, purge flows adversely affect the performance and efficiency of the turbine engine. Hence, the usage of purge air should be minimized.
As a result, there is a need for improved systems and apparatus that better seal gaps or cavities within the turbine engine. Particularly, there is a need for improved seals that reduce leakage and/or the usage of cooling air.